import React, { Component } from 'react'

export default class Count extends Component {

  state = {
    count: 0
  }

  increment = ()=> {
    const {value} = this.selectNumber
    const {count} = this.state
    this.setState({count: count + value*1})
  }

  decrement = ()=> {
    const {value} = this.selectNumber
    const {count} = this.state
    this.setState({count: count - value*1})
  }

  incrementIfOdd =()=> {
    const {value} = this.selectNumber
    const {count} = this.state
    if(count % 2 ===1) {
      this.setState({count: count + value*1})
    }
  }

  incrementAsync =()=>{
    const {value} = this.selectNumber
    const {count} = this.state
    setTimeout(()=>{
      this.setState({count: count + value*1})
    },500)
  }

  render() {
    return (
      <div>
        <h1>当前求和为: {this.state.count}</h1>
        <select ref={c=> this.selectNumber = c}>
          <option value="1">1</option>
          <option value="2">2</option>
          <option value="3">3</option>
        </select>&nbsp;
        <button onClick={this.increment}>+</button>&nbsp;
        <button onClick={this.decrement}>-</button>&nbsp;
        <button onClick={this.incrementIfOdd}>当前求和为奇数时再加</button>&nbsp;
        <button onClick={this.incrementAsync}>异步加</button>
      </div>
    )
  }
}
